Field of the Invention
This invention concerns a method of and an apparatus for forming gas supply passages in a member made of ceramics and, more specifically, it relates to a method of and apparatus for forming gas supply passages to a stationary plate or a slide plate made of a ceramic member for use in a molten metal discharging slide gate attached to the bottom portion of a ladle or tundish in the case of casting molten metals.
Upon casting molten steels by way of a conventional continuous casting process, a molten metal discharging device comprising a stationary plate and a slide plate is attached to the bottom portion of a ladle or a tundish accomodating the molten steels and the flow rate of the molten steels is adjusted by causing the slide plate to move slidably with respect to the stationary plate thereby opening or closing a passage bore for the molten steels. In the above-mentioned molten metal discharging device, an inert gas such as argon is introduced through small holes formed in the stationary plate or the slide plate to the molten steel passage bore so as to prevent the clogging in the passage bore caused by the solidification of the molten steels and/or deposition of oxides of metal such as Al, Ti, Ca, Cr, Mn, Si or Ni.
The inert gas is supplied, for instance, by disposing a gas supply member formed with a plurality of small holes each in 0.1-1.0 mm diameter or a gas supply member formed with a plurality of slits each in rectangular cross section, to a predetermined position. The small holes or slits have been formed in the plate by previously embedding hard papers or vinyl chloride wires at predetermined positions in a refractory mixed body upon molding of the plate and then burning out them during a sintering or burning step, or by forming them by drilling work after the sintering.
However, fabrication of the small holes or slits by the use of hard papers or vinyl chloride wires have beed disadvantageous in that the small holes or the slits can not always penetrate the plate completely, diameter for each of the bores may possibly vary to make the distribution of the supplied gas irregular and the work is very much labourious. While on the other hand, the drilling work is very difficult and time-consuming in the case of machining the thick material to make the machining cost more expensive.